New York-based Alcoa, best-known as an aluminum producer, said around 80 percent of RTI's business is in aerospace and defense. The acquisition is its latest move to diversify into value-added products.

"This builds out our value-added business in a very attractive market - aerospace," Alcoa Chief Executive Klaus Kleinfeld said in an interview, adding that titanium is the fastest-growing metal used in aerospace production.

Last week Alcoa completed the acquisition of Tital, a German manufacturer of titanium and aluminum structural castings for aircraft.

"Basically, we've become a titan in titanium," Kleinfeld said.

Pittsburgh-based RTI, whose customers include Boeing Co, reported revenue of $794 million in 2014, and said it expected revenue of $850 million in 2015. Alcoa expects RTI's sales to reach $1.2 billion by 2019.